title: Caseload as a factor for outcome in aneurysmal subarachnoid hemorrhage: a systematic review and meta-analysis.
abstract: OBJECTIVE
  Increasing evidence exists that treatment of complex medical conditions in high-volume centers is found to improve outcome. Patients with subarachnoid hemorrhage (SAH), a complex disease, probably also benefit from treatment at a high-volume center. The authors aimed to determine, based on published literature, whether a higher hospital caseload is associated with improved outcomes of patients undergoing treatment after aneurysmal subarachnoid hemorrhage.
  
  
  METHODS
  The authors identified studies from MEDLINE, Embase, and the Cochrane Library up to September 28, 2012, that evaluated outcome in high-volume versus low-volume centers in patients with SAH who were treated by either clipping or endovascular coiling. No language restrictions were set. The compared outcome measure was in-hospital mortality. Mortality in studies was pooled in a random effects meta-analysis. Study quality was reported according to the GRADE (Grading of Recommendations Assessment, Development and Evaluation) criteria.
  
  
  RESULTS
  Four articles were included in this analysis, representing 36,600 patients. The quality of studies was graded low in 3 and very low in 1. Meta-analysis using a random effects model showed a decrease in hospital mortality (OR 0.77 [95% CI 0.60-0.97]; p = 0.00; I(2) = 91%) in high-volume hospitals treating SAH patients. Sensitivity analysis revealed the relative weight of the 1 low-quality study. Removal of the study with very low quality increased the effect size of the meta-analysis to an OR of 0.68 (95% CI 0.56-0.84; p = 0.00; I(2) = 86%). The definition of hospital volume differed among studies. Cutoffs and dichotomizations were used as well as division in quartiles. In 1 study, low volume was defined as 9 or fewer patients yearly, whereas in another it was defined as fewer than 30 patients yearly. Similarly, 1 study defined high volume as more than 20 patients annually, and another defined it as more than 50 patients a year. For comparability between studies, recalculation was done with dichotomized data if available. Cross et al., 2003 (low volume ≤ 18, high volume ≥ 19) and Johnston, 2000 (low volume ≤ 31, high volume ≥ 32) provided core data for recalculation. The overall results of this analysis revealed an OR of 0.85 (95% CI 0.72-0.99; p = 0.00; I(2) = 87%).
  
  
  CONCLUSIONS
  Despite the shortcomings of this study, the mortality rate was lower in hospitals with a larger caseload. Limitations of the meta-analysis are the not uniform cutoff values and uncertainty about case mix.
authors.affiliation: Departments of Neurosurgery and.
authors.forename: Hieronymus D
authors.initials: HD
authors.lastname: Boogaarts
authors.forename: Martinus J
authors.initials: MJ
authors.lastname: van Amerongen
authors.forename: Joost
authors.initials: J
authors.lastname: de Vries
authors.forename: Gert P
authors.initials: GP
authors.lastname: Westert
authors.forename: André L M
authors.initials: AL
authors.lastname: Verbeek
authors.forename: J André
authors.initials: JA
authors.lastname: Grotenhuis
authors.forename: Ronald H M A
authors.initials: RH
authors.lastname: Bartels
mesh_terms: D017052:Hospital Mortality; D061847:Hospitals, High-Volume / Q000706:statistics & numerical data*; D006801:Humans; D017063:Outcome Assessment, Health Care; D013345:Subarachnoid Hemorrhage / Q000401:mortality* / Q000601:surgery*